This application is based upon and claims priority to German Patent Application 199 43 209.0 filed Sep. 9, 1999, which application is herein expressly incorporated by reference.
The invention relates to a coupling assembly for agricultural implements which includes a friction coupling.
Friction couplings are used in agricultural machinery when large masses, such as flywheels, need to be accelerated. During acceleration, the coupling slips and transforms the absorbed energy into heat. The friction coupling in such implements also reacts if a blockage occurs inside the implement. Thus, the entire friction power, or the driving power, is transformed into heat. The coupling heats up very quickly. The stored heat can only be dissipated via the coupling surface. In consequence, cooling takes a correspondingly long time. Accordingly, a great risk of the friction coupling overheating exists. This is the reason why friction couplings are used only in those cases where large masses need to be accelerated and where overloading due to blockages occurs only occasionally.
It is an object of the invention to provide a coupling assembly with a friction coupling where the risk of overheating is reduced. In consequence, the coupling has a correspondingly longer service life.
In accordance with the invention, a coupling assembly has a friction coupling which defines a longitudinal axis. The friction coupling has a housing with a first friction face positioned perpendicularly to the longitudinal axis. A hub is received in the housing. The hub is rotatable relative to the housing around the longitudinal axis. The hub is axially displaceable to a limited extent. The hub includes at least one first hub plate which is firmly connected to the hub. A pressure plate, with pressure springs, loading the pressure plate, is supported on a supporting plate secured to the housing. Friction plates are arranged between the first friction face of the housing and the first hub plate. Also, friction plates are positioned between the first hub plate and the pressure plate. Optionally, friction plates are positioned between each further plate connected to the housing and each further plate connected to the hub. An actuating device with an annular electromagnet is arranged co-axially around a portion of the hub projecting from the housing. The actuating device is rotatable relative thereto and non-adjustably supported in the direction of the longitudinal axis and securable against rotation by securing means. The actuating device includes an anchor plate which is connected by setting pins to the pressure plate. Also, the actuating device is connected to the housing in a rotationally fast way. A control mechanism is present to connect the electromagnet to a power source.
An advantage of this assembly is that, during acceleration, the transmitted torque slowly builds up to the nominal torque. Thus, a high speed differential exists. The specific surface pressure values at the beginning of the coupling process are low. Accordingly, compared to conventional solutions, less heat is generated which need to be absorbed by the coupling. Thus, the risk of the coupling overheating is reduced and the service life is increased.
A method of controlling a friction coupling exists to achieve the objective. The friction coupling includes a housing, a hub and a friction assembly loaded by a pressure plate. The pressure plate is loaded by pressure springs. The pressure plate is adjustable by an actuating device. Adjustment takes place by a control mechanism such that, within a predetermined period of time, the pressure force of the pressure plate, while starting from a minimum value, is increased to the full value of pressure application. The smallest possible minimum value is zero.
According to a further embodiment of the invention, apertures extending parallel to the longitudinal axis are formed on the circumference of the supporting plate. Setting pins are guided through each of the apertures. In the region between the pressure plate and the supporting plate, the pressure springs are received on the setting pins. Accordingly, the anchor plate is guided by the setting pins in an advantageous way. The electromagnet is preferably supported by rolling contact bearings.
The control mechanism preferably includes a control member. While the friction coupling starts to operate, the control member causes the actuating force generated by the electromagnet, acting against the force of the pressure springs, to drop from a maximum to a reduced value over a predetermined period of time. When the electromagnet no longer applies any force to the pressure plate in the load-relieving sense, the coupling is set to the nominal torque.
Additionally, a claw coupling is provided for applications requiring the operation of uncoupling the driveline to proceed over a long period of time. The claw coupling is connected in series relative to the friction coupling and to the actuating device. The claw coupling interrupts the flow of force in an energy-free way. For a lengthy disconnecting operation, the power consumption of the electromagnet would be too high.
The housing and the hub are each associated with a speed sensor to prevent the friction coupling from overheating in the case of overloading. The control mechanism includes a speed comparator and a time member. If a predetermined speed differential between the housing and the hub is exceeded, the control mechanism activates the electromagnet for a predetermined period of time to at least partially relieve the load on the friction assembly. A warning signal indicates to the operator that overloading is taking place. Thus, the signal enables the operator to stop the machine and to remove any blockages which may have resulted in overloading.
During activation of the electromagnet, to prevent the anchor plate from hitting the electromagnet and to prevent the setting pins from being bent at start up of the coupling, the anchor plate is connected to the supporting plate by fixing elements. Thus, the anchor plate is axially displaceable to a limited extent and rotationally fast.
According to a further embodiment of the inventive method, it is proposed to increase the pressure force for a predetermined time period in order to act against a reduction in the friction value when the coupling is used frequently. Also, the implement is freed in the case of a blockage. Accordingly, a second electromagnet or an additional coil are included to provide the anchor plate with additional pressure.
Furthermore, to achieve disconnection in the event of overloading, the speeds of the housing and of the hub are measured and compared. If a predetermined speed differential is exceeded over a predetermined period of time, the load on the friction assembly is relieved and a warning signal is generated.
Accordingly, the coupling assembly and method of operation with a controlled starting behavior enable the design of the drivelines connected to and following the coupling assembly to take place without taking into account the starting peaks. Even when the coupling is warm, it is possible to provide compensation during the starting process. Here, increased pressure is applied to the friction coupling. As a result, the transmission of torque by the coupling can be increased to such an extent that it corresponds to the normal starting behavior of the coupling, beginning with the cold condition.
From the following detailed description, taken in conjunction with the drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.